Light emitting diode having electrode pads

ABSTRACT

The present invention relates to light-emitting diodes. A light-emitting diode according to an exemplary embodiment of the present invention includes a first group including a plurality of first light emitting cells connected in parallel to each other, and a second group including a plurality of second light emitting cells connected in parallel to each other. Each first light emitting cell and second light emitting cell has a semiconductor stack that includes a first conductivity-type semiconductor layer, a second conductivity-type semiconductor layer, and an active layer disposed between the first conductivity-type semiconductor layer and the second conductivity-type semiconductor layer. At least two light emitting cells of the first light emitting cells share the first conductivity-type semiconductor layer, and at least two light emitting cells of the second light emitting cells share the first conductivity-type semiconductor layer. The first light emitting cells are connected in series to the second light emitting cells.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 12/963,921, filed on Dec. 9, 2010, and claims priority from andthe benefit of Korean Patent Application No. 10-2011-0080232, filed onAug. 11, 2011 and Korean Patent Application No. 10-2009-0123862, filedon Dec. 14, 2009, which are all hereby incorporated by reference for allpurposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Exemplary embodiments of the present invention relate to light-emittingdiodes and to light-emitting diodes having electrode pads, and moreparticularly, to high voltage and/or high efficiency light-emittingdiodes.

2. Discussion of the Background

Gallium nitride (GaN) based light emitting diodes (LEDs) have been usedin a wide range of applications including full color LED displays, LEDtraffic signals, and white LEDs.

The GaN-based light emitting diode may be generally formed by growingepitaxial layers on a substrate, for example, a sapphire substrate, andincludes an N-type semiconductor layer, a P-type semiconductor layer,and an active layer disposed between the N-type semiconductor layer andthe P-type semiconductor layer. Further, an N electrode pad is formed onthe N-type semiconductor layer and a P electrode pad is formed on theP-type semiconductor layer. The light emitting diode is electricallyconnected to and operated by an external power source through theseelectrode pads. Here, electric current is directed from the P-electrodepad to the N-electrode pad through the semiconductor layers.

Generally, since the P-type semiconductor layer may have a highresistivity, electric current may not be evenly distributed within theP-type semiconductor layer, but may be concentrated on a portion of theP-type semiconductor layer where the P-electrode pad is formed. Electriccurrent may be concentrated on and flow through edges of thesemiconductor layers. This may be referred to as current crowding, andmay lead to a reduction in light emitting area, thereby deterioratingluminous efficacy of a source. A transparent electrode layer having alow resistivity may be formed on the P-type semiconductor layer toenhance current spreading. In this structure, electric current suppliedfrom the P-electrode pad may be dispersed by the transparent electrodelayer before entering the P-type semiconductor layer, thereby increasinga light emitting area of the LED.

However, since the transparent electrode layer may tend to absorb light,the is thickness of the transparent electrode layer is limited, therebyproviding limited current spreading. In particular, for a large LEDhaving an area of about 1 mm² or more, there is a limitation on currentspreading through the transparent electrode layer.

To facilitate current spreading within a LED, extensions extending fromthe electrode pads may be used. For example, U.S. Pat. No. 6,650,018,issued to Zhao, et al. discloses an LED that includes a plurality ofextensions extending in opposite directions from electrode pads toenhance current spreading. Although the use of extensions may enhancecurrent spreading over a wide region of the LED, current crowding maystill occur at portions of the LEDs where the electrode pads are formed.

Moreover, as the size of the LED increases, the likelihood of a defectbeing present in the light emitting diode may increase. Defects such asthreading dislocations, pin-holes, etc. provide a path through whichelectric current may flow rapidly, thereby disturbing uniform currentspreading in the LED.

A light emitting device having a plurality of light emitting cellsserially connected to each other in a single chip to operate under highvoltage is disclosed in U.S. Pat. No. 7,417,259, issued to Sakai, et al.

Recently, light emitting devices capable of being powered by 110 V or220 V domestic alternating current (AC) power sources have beencommercialized. In such a light emitting device, chips each having aplurality of light emitting cells serially connected to each other aremounted in a package to be serially connected to each other, and eachpackage may be used together with a bridge rectifier. Two to four lightemitting diode chips, each of which includes sixteen to twenty lightemitting cells serially connected to each other on a single substrate,may be connected in series within a package to be powered by 110 V or220 V power sources.

Particularly, assuming that each light emitting cell is powered by aforward voltage of about 3.5V, three to fifteen light emitting cells areserially connected to each other in order to provide high voltageproducts, such as 12V, 24V, 36V, 48V, and the like, to which a switchingmode power supply (SMPS) is applied. Since a power of about 3 to 11 Wmay be applied to high voltage products, relatively high electriccurrent may be supplied to each of the light emitting cells. In thiscase, if the light emitting cells have excessively small sizes, currentdensity may be excessively increased, thereby deteriorating reliability.On the contrary, if the light emitting cells have excessively largesizes, electric current may not be uniformly distributed, therebycausing current crowding and deteriorating light extraction efficiency.

FIG. 7 is a schematic plan view explaining a conventional high voltagelight emitting diode and FIG. 8 is a schematic circuit diagram of FIG.7. Here, three light emitting cells are connected in series.

Referring to FIG. 7 and FIG. 8, a conventional light emitting diodeincludes a substrate 21, light emitting cells C1, C2, C3, a cathode 37,an anode 39, interconnecting sections 41, first electrode pads 35, andsecond electrode pads 33.

The light emitting cells C1, C2, C3 are separated from each other on thesubstrate 21 and each includes a first conductive type semiconductorlayer 23, an active layer (not shown), and a second conductive typesemiconductor layer 27. Here, the first conductive type semiconductorlayer 23 is an n-type semiconductor layer, and the second conductivetype semiconductor layer 27 is a p-type semiconductor layer. In thelight emitting cells C1, C2, C3, the first conductive type semiconductorlayers 27 are separated from each other, so that each of the lightemitting cells C1, C2, C3 constitutes each unit U1, U2, U3. Atransparent electrode layer (not shown) may be placed on the secondconductive type semiconductor layer 27.

The cathode 37 is placed on the first conductive type semiconductorlayer 23 of each of the light emitting cells Cl, C2, C3, and the anode39 is also placed on the second conductive type semiconductor layer 27of each of the light emitting cells Cl, C2, C3. The cathodes 37 and theanodes 39 may be distributed in alternate arrangement over a wide areafor current spreading.

Meanwhile, in adjacent light emitting cells, the cathode 37 is seriallyconnected to the anode 39 via the interconnecting section 41.Accordingly, as shown in FIG. 8, it is possible to provide a lightemitting diode having three serially connected light emitting cells andpowered by, for example, a 12V power source.

In this light emitting diode, two first electrode pads 35 and two secondelectrode pads 33 are provided for current spreading, and the anode 39and cathode 37 extend on each of the light emitting cells C1, C2, C3.

However, since the anode 39 and the cathode 37 are formed to relativelylarge sizes in order to obtain uniform current spreading on a largescale chip having, for example, a size of 1 mm×1 mm or more, opticalloss inevitably occurs due to the anode and cathode 37, 39. Furthermore,since a relatively long anode 39 is placed on a single light emittingcell, current crowding is likely to occur near the second electrode pads33. Moreover, since each light emitting cell has a relatively largelight emitting area, light extraction efficiency is further deteriorateddue to low current density.

On the other hand, for a light emitting diode in which a relativelylarge number of light emitting cells, for example, 15 light emittingcells, are serially connected in each of chips having the same size, thelight emitting cells have small sizes so that current density increasesin the light emitting cells, thereby deteriorating reliability.

SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention provide a light emittingdiode which ensures uniform current spreading in light emitting cells.

Exemplary embodiments of the present invention also provide a lightemitting diode capable of improving light extraction efficiency of eachlight emitting cell.

Exemplary embodiments of the present invention also provide a lightemitting diode having high reliability.

Exemplary embodiments of the invention also provide a light emittingdiode with high integration of light emitting cells.

Additional features of the invention will be set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention.

An exemplary embodiment of the present invention discloses a lightemitting diode including a first group including a plurality of firstlight emitting cells connected in parallel to each other, and a secondgroup including a plurality of second light emitting cells connected inparallel to each other. Each of the first and second light emittingcells has a semiconductor stack which includes a first conductivity-typesemiconductor layer, a second conductivity-type semiconductor layer, andan active layer disposed between the first conductivity-typesemiconductor layer and the second conductivity-type semiconductorlayer. At least two light emitting cells of the first light emittingcells share the first conductivity-type semiconductor layer, and atleast two light emitting cells of the second light emitting cells sharethe first conductivity-type semiconductor layer. The first lightemitting cells are connected in series to the second light emittingcells.

An exemplary embodiment of the present invention also discloses a lightemitting diode including a first group of first light emitting cellsincluding a plurality of pairs of first light emitting cells, the lightemitting cells in each pair facing each other, a first common cathodeline connected to each pair of first light emitting cells, and firstanode lines respectively connected to the first light emitting cells ata first side and a second side in each pair of first light emittingcells. Each of the first light emitting cells includes a firstconductivity-type semiconductor layer, an active layer, and a secondconductivity-type semiconductor layer, and each pair of first lightemitting cells shares the first conductivity-type semiconductor layer.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a plan view of a light emitting diode according to anexemplary embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along line A-A of FIG. 1.

FIG. 3 is a cross-sectional view taken along line B-B of FIG. 1.

FIG. 4 is a cross-sectional view of a light emitting diode according toan exemplary embodiment of the present invention.

FIG. 5 is a plan view of a light emitting diode according to anexemplary embodiment of the present invention.

FIG. 6 is a plan view of a light emitting diode according to anexemplary embodiment of the present invention.

FIG. 7 is a schematic plan view of a conventional light emitting diode.

FIG. 8 is a circuit diagram of FIG. 7.

FIG. 9 is a schematic plan view of a light emitting diode in accordancewith an exemplary embodiment of the present invention.

FIG. 10 is a circuit diagram of FIG. 9.

FIG. 11 a and FIG. 11 b are sectional views taken along lines A-A andB-B of FIG. 9.

FIG. 12 is a schematic plan view of a light emitting diode in accordancewith an exemplary embodiment of the present invention.

FIG. 13 is a circuit diagram of FIG. 12.

FIG. 14 a and FIG. 14 b are sectional views taken along lines A-A andB-B of FIG. 12.

FIG. 15 is a schematic plan view of a light emitting diode in accordancewith an exemplary embodiment of the present invention.

FIG. 16 is a circuit diagram of FIG. 15.

FIG. 17 a and FIG. 17 b are sectional views taken along lines A-A andB-B of FIG. 15.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The invention is described more fully hereinafter with reference to theaccompanying drawings, in which exemplary embodiments of the inventionare shown. This invention may, however, be embodied in many differentforms and should not be construed as limited to the exemplaryembodiments set forth herein. Rather, these exemplary embodiments areprovided so that this disclosure is thorough and will fully convey thescope of the invention to those skilled in the art. In the drawings, thesizes and relative sizes of layers and regions may be exaggerated forclarity. Like reference numerals in the drawings denote like elements.

It will be understood that when an element such as a layer, film, regionor substrate is referred to as being “on” another element, it can bedirectly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” another element, there are no intervening elements present.

FIG. 1 is a plan view of a light emitting diode according to anexemplary embodiment of the present invention, FIG. 2 is across-sectional view taken along line A-A of FIG. 1, and FIG. 3 is across-sectional view taken along line B-B of FIG. 1.

Referring to FIG. 1, FIG. 2, and FIG. 3, the light emitting diodeincludes a substrate 21, a first conductive type semiconductor layer 23,an active layer 25, a second conductive type semiconductor layer 27, aninsulation layer 31, first electrode pad 35, second electrode pad 33,and upper extensions 33 a. The light emitting diode may further includeconnecting portions 33 b, a transparent electrode layer 29, and lowerextensions 35 a. The substrate 11 may be a sapphire substrate, but isnot limited thereto.

The first conductive type semiconductor layer 23 is located on thesubstrate 21 and the second conductive type semiconductor layer 27 islocated on the first conductive type semiconductor layer 23 with theactive layer 25 disposed between the first and second conductive typesemiconductor layers 23 and 27. The first conductive type semiconductorlayer 23, active layer 25, and second conductive type semiconductorlayer 27 may be formed of, but are not limited to, a GaN-based compoundsemiconductor material such as (Al, In, Ga)N. The constituent elementsand composition of the active layer 25 are determined to emit lighthaving a desired wavelength, for example, ultraviolet or blue light. Thefirst conductive type semiconductor layer 23 may be an n-type nitridesemiconductor layer and the second conductive type semiconductor layer27 may be a p-type nitride semiconductor layer, or vice versa.

The first conductive type semiconductor layer 23 and/or the secondconductive type semiconductor layer 27 may have a single layerstructure, or alternatively, a multilayer structure. Further, the activelayer 25 may have a single quantum well structure or a multi-quantumwell structure. The light emitting diode may further include a bufferlayer (not shown) disposed between the substrate 21 and the firstconductive type semiconductor layer 23. These first conductive typesemiconductor layer 23, the active layer 25, and the second conductivetype semiconductor layer 27 may be formed by a metal-organic chemicalvapor deposition (MOCVD) technique or molecular beam epitaxy (MBE)technique.

A transparent electrode layer 29 may be formed on the second conductivetype semiconductor layer 27. The transparent electrode layer 29 may beformed of indium tin oxide (ITO) or Ni/Au, and form an ohmic contactwith the second conductive type semiconductor layer 27.

The second conductive type semiconductor layer 27 and the active layer25 may be subjected to a process to expose a region(s) of the firstconductive type semiconductor layer 23 via photolithography and etching.Such a process is generally known as a mesa-etching. The mesa etchingmay provide divided light emitting regions as shown in FIG. 1 and FIG.2. Although, in the present exemplary embodiment, the light emittingdiode has two light emitting regions that are isolated from each other,the light emitting diode may have more than two separate light emittingregions. Further, the mesa-etching may be performed to form inclinedside surfaces which have a degree of inclination in the range of 30-70degrees.

The first electrode pad 35 and the second electrode pad 33 are locatedon the first conductive type semiconductor layer 23, which is exposedthrough the mesa etching. The first electrode pad 35 is electricallyconnected to the first conductive type semiconductor layer 23. Thesecond electrode pad 33 is insulated from the first conductive typesemiconductor layer 23 by the insulation layer 31. The first electrodepad 35 and the second electrode pad 33 are bonding pads for bondingwires and may have an area sufficiently wide for wire bonding. The firstelectrode pad 35 and the second electrode pad 33 may be formed on theexposed region(s) of the first conductive type semiconductor layer 23,but are not limited thereto.

The insulation layer 31 is disposed between the second electrode pad 33and the first conductive type semiconductor layer 23 to insulate thesecond electrode pad 33 from the first conductive type semiconductorlayer 23. Further, the insulation layer 31 may cover the side surfacesof the second conductive type semiconductor layer 27 and the activelayer 25, which are exposed by the mesa etching. The insulation layer 31may extend to an upper surface of the second conductive typesemiconductor layer 27 such that an edge of the insulation layer 31overlaps the second conductive type semiconductor layer 27 or thetransparent electrode layer 29. The insulation layer 31 may be a singlelayer structure (as shown in the Figures), or a multilayered structure.The insulation layer 31 may include, for example, SiO₂ and/or Si₃N₄.Alternatively, the insulation layer 31 may be a multilayered dielectricreflector (such as a distributed Bragg reflector), including alternatelystacked layers of SiO₂ and TiO₂. The multilayered dielectric reflectorcan reflect light incident on the second electrode pad 33, thusdecreasing light absorption by the second electrode pad 33.

The upper extensions 33 a are located on the second conductive typesemiconductor layer 27 (or transparent electrode layer 29). The upperextensions 33 a may be connected to the second electrode pad 33 viaconnecting portions 33 b, respectively, and may be electricallyconnected to the second conductive type semiconductor layer 27. Theupper extensions 33 a are disposed to allow uniform current spreading onthe second conductive type semiconductor layer 27. The connectingportions 33 b are separated from the side surfaces of the transparentelectrode layer 29, the second conductive type semiconductor layer 27,and the active layer 25 by the insulation layer 31.

At least one lower extension 35 a may extend from the first electrodepad 35. The lower extension 35 a is located on the first conductive typesemiconductor layer 23 and electrically connected thereto. As shown inthe figures, the lower extension 35 a may be located between the dividedlight emitting regions, but is not limited thereto. Alternatively, thelower extension 35 a may be located outside the light emitting regions.

As shown in the present exemplary embodiment as well as the followingexemplary embodiments, the lower extension 35 a and the upper extension33 a may be arranged in specific patterns to help improve currentspreading. For example, in the present exemplary embodiment, having twoupper extensions 33 a extend from the second electrode pad 33 along eachof the divided light emitting regions may improve current spreadingwhile not requiring multiple electrode pads on the light emitting diodeto connect to the upper extensions 33 a. In the various exemplaryembodiments, the lower extension and upper extension arrangement maylikewise improve current spreading in divided light emitting regionswhile avoiding a requirement for multiple electrode pads on the singlesubstrate.

The second electrode pad 33, the first electrode pad 35, the upperextensions 33 a, the connecting portions 33 b, and the lower extension35 a may be formed of, but are not limited to, the same material, forexample, Cr/Au by the same process. Alternatively, the upper extensions33 a and the second electrode pad 33 may be formed of differentmaterials by different processes.

In the present exemplary embodiment, the divided light emitting regionshave a symmetrical structure relative to a line, for example, a cut lineB-B, which is located between the first electrode pad 35 and the secondelectrode pad 33. The upper extensions 33 a are also disposed in asymmetrical structure, so that the light emitting regions may exhibitthe same radiation characteristics. Accordingly, when a light emittingregion is divided into two light emitting regions in a single lightemitting diode, a process of packaging the light emitting diode may befurther simplified compared to using two light emitting diodes connectedin parallel to each other. Furthermore, the divided light emittingregions may relieve current crowding caused by defects and may improvelight extraction efficiency through formation of the inclined sidesurfaces by mesa etching.

FIG. 4 shows a cross-sectional view of a light emitting diode accordingto an exemplary embodiment of the present invention.

Referring to FIG. 4, the light emitting diode of the present exemplaryembodiment is generally similar to the light emitting diode describedwith reference to FIG. 1, FIG. 2, and FIG. 3. In the light emittingdiode of the present exemplary embodiment, however, a portion of asecond electrode pad 43 is located on a second conductive typesemiconductor layer 27.

Specifically, the second electrode pad 43 is located on a firstconductive type semiconductor layer 23 exposed through a mesa etchingprocess and a portion of the second electrode pad 43 is located on thesecond conductive type semiconductor layer 27. The second electrode pad43 is insulated not only from the first conductive type semiconductorlayer 23 but also from the transparent electrode layer 29, the secondconductive type semiconductor layer 27, and the active layer 25 by aninsulation layer 31. Extensions 33 a extend from the second electrodepad 43.

In the present exemplary embodiment, the second electrode pad 43 isseparated from the semiconductor layers by the insulation layer 31,which may thereby prevent current crowding around the second electrodepad 43. Furthermore, in the present exemplary embodiment, an areasubjected to mesa etching may be decreased compared to the previousexemplary embodiment, thereby increasing the light emitting region.

FIG. 5 is a plan view of a light emitting diode according to anexemplary embodiment of the present invention.

In the exemplary embodiment shown in FIG. 1, the first electrode pad 35and the second electrode pad 33 are disposed along a major axis of thelight emitting diode, and the light emitting regions are divided fromeach other along the major axis of the light emitting diode. On thecontrary, the light emitting diode according to the present exemplaryembodiment includes a first electrode pad 55 and a second electrode pads53 disposed along a minor axis of the light emitting diode and lightemitting regions divided from each other along the minor axis of thelight emitting diode. Further, the divided light emitting regions aredisposed in a symmetrical structure and upper extensions 53 a and lowerextensions 55 a are also disposed in a symmetrical structure.

In the present exemplary embodiment, the upper extensions 53 a extendalong a periphery of the light emitting diode to surround the lightemitting diode, and each of the upper extensions 53 a has an extension53 b extending inward from the periphery of the light emitting diode.The lower extensions 55 a extend from an inner side of the lightemitting diode toward the outside of the light emitting diode. Each ofthe lower extensions 55 a may be bifurcated to surround an extension 53b in each light emitting region. In the present exemplary embodiment,the ends of lower extensions 55 a have a shape which resembles a “U”,but is not limited thereto.

FIG. 6 is a plan view of a light emitting diode according to anexemplary embodiment of the present invention.

Referring to FIG. 6, the light emitting diode of the present exemplaryembodiment is generally similar to the light emitting diode describedwith reference to FIG. 5. In the light emitting diode of the presentexemplary embodiment, however, lower extensions 65 a and upperextensions 63 a have different arrangements than the upper extensions 53a and lower extensions 55 a.

Specifically, the lower extensions 65 a extend along a periphery of thelight emitting diode first and then extend into the light emittingregions, and each of the upper extensions 63 a includes two extensionportions disposed on one of the light emitting regions, and these twoextension portions surround the lower extension 65 a extending into thelight emitting region. That is, in the present exemplary embodiment, afirst portion of each upper extension 63 a extends along a periphery ofthe light emitting region, and a second portion of each upper extension63 a extends into the light emitting region after branching off from thefirst portion of the upper extension 63 a. A part of the second portionof the upper extension 63 a extending into the light emitting region issubstantially perpendicular to the lower extension 65 a extending intothe light emitting region, and another part of the second portion of theupper extension 63 a extending into the light emitting region issubstantially parallel to the lower extension 65 a extending into thelight emitting region. Therefore, the two portions of the upperextension 63 a may be referred to as surrounding the lower extension 65a extending into the light emitting region. This arrangement may improvecurrent spreading in the divided light emitting regions in the lightemitting diode.

Although exemplary embodiments are described above to illustrate thepresent invention, the light emitting diode is described as beingdivided into two light emitting regions, but alternative embodiments mayhave the light emitting diode being divided into more than two lightemitting regions. In some embodiments, the light emitting regions maynot be completely divided from each other. In other words, portions ofthe light emitting regions may be connected to each other.

FIG. 9 is a schematic plan view of a light emitting diode in accordancewith an exemplary embodiment of the present invention, FIG. 10 is acircuit diagram of FIG. 9, and FIG. 11 a and FIG. 11 b are sectionalviews taken along lines A-A and B-B of FIG. 9.

Referring to FIG. 9, FIG. 10, FIG. 11 a, and FIG. 11 b, the lightemitting diode according to the present exemplary embodiment includes asubstrate 21, a plurality of light emitting cells 26, first to thirdcommon electrode lines CL1, CL2, CL3, first to third electrode linesAL1, AL2, AL3, interconnecting sections 71, a first electrode pad 65,and a second electrode pad 63. Further, a transparent electrode layer 29may be placed on each of the light emitting cells 26, and an insulatinglayer 61 may be formed on upper and lateral sides of each of the lightemitting cells 26.

The substrate 21 supports the light emitting cells 26, and may be agrowth substrate for growing semiconductor layers, which includes, butis not limited to, a sapphire substrate, a silicon substrate, and a GaNsubstrate. Typically, the substrate 21 refers to a substrate in a lightemitting diode chip. However, when there is no substantial substratewithin a chip, the substrate 21 refers to a substrate which directlysupports a light emitting structure.

The plurality of light emitting cells 26 is placed on the substrate 21.As shown in FIG. 11 a and FIG. 11 b, each of the light emitting cells 26includes a first conductive type semiconductor layer 23, an active layer25, and a second conductive type semiconductor layer 27. In the presentexemplary embodiment, the first conductive type semiconductor layer 23is an n-type semiconductor layer and the second conductive typesemiconductor layer 27 is a p-type semiconductor layer. Alternatively,the first conductive type semiconductor layer 23 may be a p-typesemiconductor layer and the second conductive type semiconductor layer27 may be an n-type semiconductor layer. The active layer 25 is locatedbetween the first conductive type semiconductor layer 23 and the secondconductive type semiconductor layer 27 and may have a single quantumwell structure or multi-quantum well structure. The active layer 25 maybe formed of a material having a composition depending on desiredwavelengths. For example, the active layer 25 may be formed of anAlInGaN-based compound semiconductor, for example, InGaN. On the otherhand, the first and second conductive type semiconductor layer 23, 27may include an AlInGaN-based compound semiconductor, for example, GaN,which has a greater energy band gap than that of the active layer 25. Abuffer layer (not shown) may be interposed between the first conductivetype semiconductor layer 23 and the substrate 21.

The first conductive type semiconductor layer 23, active layer 25 andsecond conductive type semiconductor layer 27 may be grown on thesubstrate 21 by metal organic chemical vapor deposition, followed bypatterning through photolithography and etching.

Referring again to FIG. 9 and FIG. 10, the light emitting cells 26 areregularly arranged on the substrate 21. Here, each pair of lightemitting cells is constituted by the light emitting cells disposed toface each other except for the light emitting cell C1 to which a secondelectrode pad 63 is connected, and each pair of light emitting cellsshares the first conductive type semiconductor layer 23. For example, afirst row on which the second electrode pad 63 is placed includes pairsof first light emitting cells C11 and C12 disposed to face each other, asecond row includes pairs of second light emitting cells C21 and C22disposed to face each other, and a third row includes pairs of thirdlight emitting cells C31 and C32 disposed to face each other.

As such, each of the rows includes plural pairs of light emitting cells.On the other hand, the light emitting cell C1 is provided as a singlelight emitting cell in order to provide space for the second electrodepad 63 instead of constituting a pair with another light emitting cell.In FIG. 10, U11˜U14, U21˜U24 and U31˜U34 indicate the light emittingcells for the respective first conductive type semiconductor layers 23separated from each other in each row. The first conductive typesemiconductor layers 23 may be separated from each other not onlybetween the rows but also within in each row.

The first, second and third common electrode lines CL1, CL2, CL3 arecommonly connected to the first conductive type semiconductor layers 23of the light emitting cells 26 in the first, second and third rows,respectively. If the first conductive type semiconductor layer 23 is ann-type semiconductor, the common electrode lines CL1, CL2, CL3 arecathode lines. Each of the first, second and third common electrodelines CL1, CL2, CL3 may include an electrode 67 a connected to the firstconductive type semiconductor layer 23 and a connecting section 67 bwhich connect the electrodes 67 a to each other.

Further, the first common electrode line CL1 may be placed between thepair of first light emitting cells C11 and C12, the second commonelectrode line CL2 may be placed between the pair of second lightemitting cells C21 and C22, and the third common electrode line CL3 maybe placed between the pair of third light emitting cells C31 and C32. Inother words, the first light emitting cells C11 and C12 may be disposedto face each other with respect to the first common electrode line CL1,and the second light emitting cells C21 and C22 may be disposed to faceeach other with respect to the second common electrode line CL2.Further, the third light emitting cells C31 and C32 may be disposed toface each other with respect to the third common electrode line CL3.

Also, first electrode lines AL1 electrically connect the first lightemitting cells C11 and the first light emitting cells C12 to each otherat both sides of the first common electrode line CL1, second electrodelines AL2 electrically connect the second light emitting cells C21 andthe second light emitting cells C22 to each other at both sides of thesecond common electrode line CL1, third electrode lines AL3 electricallyconnect the third light emitting cells C31 and the third light emittingcells C32 to each other at both sides of the third common electrode lineCL3. Each of the electrode lines AL1, AL2, AL3 may include an electrode69 a connected to the second conductive type semiconductor layer 27 ineach of the light emitting cells 26 and a connecting section 69 b whichconnects the electrodes 69 a to each other. When the second conductivetype semiconductor layers 27 are p-type semiconductors, the electrodelines AL1, AL2, AL3 are anode lines.

Ends of the first electrode lines AL1 are connected to the secondelectrode pad 63. On the other hand, the first common electrode line CL1is connected to the second electrode lines AL2 via an interconnectingsection 71, and the second common electrode line CL2 is connected to thethird electrode lines AL3 via an interconnecting section 71. The thirdcommon electrode line CL3 is connected at one end thereof to the firstelectrode pad 65.

Accordingly, as shown in FIG. 10, a first group G1 includes the lightemitting cells C1, C11, C12 connected in parallel to each other betweena first node n1 and a second node n2, a second group G2 includes thelight emitting cells C21, C22 connected in parallel to each otherbetween the second node n2 and a third node n3, a third group G3includes the light emitting cells C31, C32 connected in parallel to eachother between the third node n3 and a fourth node n4. Further, the lightemitting cells C1, C11, C12 in the first group G1 are connected inseries to the light emitting cells C21, C22 in the second group G2through the second node n2, and the light emitting cells C21, C22 in thesecond group G2 are connected in series to the light emitting cells C31,C32 in the third group G3.

During operation, electric current flows into the second electrode pad63 and then flows to the first electrode pad 65 through the first,second and third nodes n1, n2, n3, so that all of the first to thirdlight emitting cells 26 are operated.

Referring again to FIG. 11 a and FIG. 11 b, a transparent electrodelayer 29 may be formed on each of the light emitting cells 26, and theelectrodes 69 a may be placed on the transparent electrode layer 29 tobe connected to the second conductive type semiconductor layers 27.Further, an insulating layer 61 may cover upper and lateral sides ofeach of the light emitting cells 26. The insulating layer 61 may beformed with openings through which the first electrode pad 65 and theelectrodes 69 a can be connected to the transparent electrode layer 29.Further, the insulating layer 61 may have openings which expose thefirst conductive type semiconductor layers 23 such that the electrodes67 a can be connected to the first conductive type semiconductor layers23. The connecting sections 69 b are insulated from the lateral sides ofthe light emitting cells 26 by the insulating layer 61.

According to the present exemplary embodiment, it is possible to providehigh integration of light emitting cells in a small chip using the lightemitting cells C11 and C12; C21 and C22; C31 and C32, which share thefirst conductive type semiconductor layer 23. In addition, it ispossible to provide a simple chip structure by arranging light emittingcells to be connected in parallel to each other in each row. Further, itis possible to ensure uniform current spreading by reducing the lengthof electrodes in the light emitting cells.

Although the present exemplary embodiment is illustrated as includingthree rows each having pairs of light emitting cells, the number of rowsmay be increased or decreased to control voltage to be applied to therespective light emitting cells depending on available voltage. Further,although the present exemplary embodiment is also illustrated asincluding seven or eight light emitting cells 26 connected in parallelto each other, the number of pairs in each row may be increased ordecreased depending upon operation current to adjust the number of lightemitting cells connected in parallel to each other. Accordingly, it ispossible to secure optimal light extraction efficiency by controllingcurrent density of the respective light emitting cells 26.

On the other hand, although the present exemplary embodiment isillustrated as including the light emitting cells 26 connected inparallel to each other in each row, the invention is not limitedthereto. For example, some of the light emitting cells in each row maybe connected in parallel to each other, and the light emitting cells intwo different rows may be connected in parallel to each other.

FIG. 12 is a schematic plan view of a light emitting diode in accordancewith an exemplary embodiment of the present invention, FIG. 13 is acircuit diagram of FIG. 12, and FIG. 14 a and FIG. 14 b are sectionalviews taken along lines A-A and B-B of FIG. 12.

Referring to FIG. 12, FIG. 13, FIG. 14 a and FIG. 14 b, the lightemitting diode according to the present exemplary embodiment isgenerally similar to the light emitting diode described with referenceto FIG. 10 and FIG. 11. In the present exemplary embodiment, however,light emitting cells 26 to which a second electrode pad 63 is connectedare also provided as a pair.

Specifically, in the exemplary embodiment shown in FIG. 10, the secondelectrode pad 63 is connected to a single light emitting cell C1,instead of being connected to a pair of light emitting cells C1, unlikethe first light emitting cells C11, C12. On the contrary, in theexemplary embodiment shown in FIG. 12, a second electrode pad 63 isconnected to a pair of first light emitting cells disposed to face eachother and sharing a first conductive type semiconductor layer 23. In thepresent exemplary embodiment, the second electrode pad 63 is formedabove the first conductive type semiconductor layer 23 and is alsoplaced on an insulating layer 61 to be insulated from the firstconductive type semiconductor layer 23 by the insulating layer 61, asshown in FIG. 14 a.

FIG. 14 b is a sectional view taken along line B-B of FIG. 12 andcorresponds to FIG. 11 b.

According to the present exemplary embodiment, each group may includethe same number of light emitting cells 26 connected in parallel to eachother, thereby making it possible to control the same electric currentto be applied to the light emitting cells 26.

FIG. 15 is a schematic plan view of a light emitting diode in accordancewith an exemplary embodiment of the invention, FIG. 16 is a circuitdiagram of FIG. 15, and FIG. 17 a and FIG. 17 b are sectional viewstaken along lines A-A and B-B of FIG. 15.

Referring to FIG. 15, FIG. 16, FIG. 17 a and FIG. 17 b, the lightemitting diode according to the present exemplary embodiment isgenerally similar to the light emitting diode described with referenceto FIG. 10 and FIG. 11. In the present exemplary embodiment, however,all of light emitting cells 26 in each of groups G1, G2, G3 share afirst conductive type semiconductor layer 23.

Specifically, in the above exemplary embodiments, the first conductivetype semiconductor layers 23 for the pairs of light emitting cells 26 ineach of the groups G1, G2, G3 are separated from each other. On thecontrary, in the present exemplary embodiment, all of the light emittingcells 26 connected in parallel to each other in each of the groups G1,G2, G3 are placed on a single first conductive type semiconductor layer23. For example, in the exemplary embodiment of FIG. 10, U11˜U14,U21˜U24, and U31˜U34 indicate the light emitting cells 26 for therespective first conductive type semiconductor layers 23 separated fromeach other in each row. On the contrary, in the present exemplaryembodiment, U11˜U14 indicate pairs of light emitting cells 26 disposedto face each other, instead of the light emitting cells 26 for therespective first conductive type semiconductor layers 23 separated fromeach other.

According to the present exemplary embodiment, it is possible to providea simpler patterning process for the first conductive type semiconductorlayers 23 and to eliminate the connecting sections 67 b. In addition, asthe pattern of first conductive type semiconductor layers 23 issimplified, the connecting sections 69 b may be formed more easily.

Furthermore, in the light emitting diode described in FIG. 12 to FIG.14, all of light emitting cells 26 connected in parallel to each otherin each group may share the first conductive type semiconductor layer23.

According to the exemplary embodiments of the present invention, thelight emitting diode ensures uniform current spreading in light emittingcells. In addition, the light emitting diode has high reliability byimproving light extraction efficiency of each light emitting cell.Further, the light emitting diode permits high integration of plurallight emitting cells by arrangement of plural pairs of light emittingcells using common cathodes.

Although the invention has been illustrated with reference to someexemplary embodiments in conjunction with the drawings, it will beapparent to those skilled in the art that various modifications andchanges can be made in the invention without departing from the spiritand scope of the invention. Therefore, it should be understood that theexemplary embodiments are provided by way of illustration only and aregiven to provide complete disclosure of the invention and to providethorough understanding of the invention to those skilled in the art.Thus, it is intended that the invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A light-emitting diode, comprising: a first groupcomprising first light emitting cells connected in parallel to eachother; a second group comprising second light emitting cells connectedin parallel to each other; a first common electrode line disposedbetween the first light emitting cells; two second electrode linesrespectively disposed on and extending across each of the second lightemitting cells; an interconnecting section electrically connecting thefirst common electrode line and the two second electrode lines; andanother two second electrode lines disposed on the first light emittingcells, wherein each first light emitting cell and second light emittingcell comprises a semiconductor stack comprising a firstconductivity-type semiconductor layer, a second conductivity-typesemiconductor layer, and an active layer disposed between the firstconductivity-type semiconductor layer and the second conductivity-typesemiconductor layer, wherein the first common electrode line isconnected to the first conductivity-type semiconductor layer of each ofthe first light emitting cells, wherein at least two light emittingcells of the first light emitting cells share the firstconductivity-type semiconductor layer, wherein at least two lightemitting cells of the second light emitting cells share the firstconductivity-type semiconductor layer, and wherein the first group iselectrically connected in series to the second group by theinterconnecting section.
 2. The light-emitting diode of claim 1, whereinthe first group comprises at least one pair of first light emittingcells disposed to face each other with respect to the first commonelectrode line, the at least one pair of first light emitting cellssharing the first conductivity-type semiconductor layer.
 3. Thelight-emitting diode of claim 2, wherein the first group comprises pairsof first light emitting cells.
 4. The light-emitting diode of claim 2,further comprising: a second common electrode line connected to thefirst conductivity-type semiconductor layers of the second lightemitting cells, wherein the second group comprises at least one pair ofsecond light emitting cells disposed to face each other with respect tothe second common electrode line, the at least one pair of second lightemitting cells sharing the first conductivity-type semiconductor layer.5. The light-emitting diode of claim 4, wherein the second groupcomprises pairs of second light emitting cells.
 6. The light-emittingdiode of claim 4, further comprising: two first electrode lines disposedon opposing sides of the first common electrode line, the two firstelectrode lines electrically connecting the second conductivity-typesemiconductor layers of the first light emitting cells to each other;and wherein the two second electrode lines are disposed on opposingsides of the second common electrode line, the two second electrodelines electrically connecting the second conductivity-type semiconductorlayers of the second light emitting cells to each other.
 7. Thelight-emitting diode of claim 1, wherein the first light emitting cellsand the second light emitting cells are disposed on a single substrate.8. The light-emitting diode of claim 1, wherein the first light emittingcells are connected in parallel to each other between a first node and asecond node, the second light emitting cells are connected in parallelto each other between the second node and a third node, and the firstlight emitting cells are connected in series to the second lightemitting cells though the second node.
 9. The light-emitting diode ofclaim 1, further comprising: a third group comprising third lightemitting cells connected in parallel to each other, wherein at least twolight emitting cells of the third light emitting cells share the firstconductivity-type semiconductor layer, and the second light emittingcells are connected in series to the third light emitting cells.
 10. Thelight-emitting diode of claim 1, further comprising an electrode paddisposed on the first conductivity-type semiconductor layer of one ofthe first light emitting cells.
 11. The light-emitting diode of claim10, wherein further comprising an insulation layer disposed between theelectrode pad and the first conductivity-type semiconductor layer,wherein the insulation layer insulates the electrode pad from the firstconductivity-type semiconductor layer.
 12. The light-emitting diode ofclaim 11, wherein the insulation layer covers a side surface of thefirst conductivity-type semiconductor layer.
 13. The light-emittingdiode of claim 9, wherein: the second group is disposed between thefirst and third groups; the first, second, and third groups areconnected in series with each other; and current is configured to travelthrough the first and third groups in a first direction and through thesecond group in a second direction opposite to the first and thirdgroups.